I've seen some scary adaptors. In Europe the EU should really have passed directives setting minimum standards for these things. I've seen some very scary universal adaptors that should be outlawed.
There are some good quality Schuko to BS1363 adaptors on the market that seem to pretty much mimic a german outlet perfectly and have proper fusing etc and a sturdy BS1363 front end..
I can't say the same for BS1363 to Schuko adaptors. Most of them don't complete the grounding properly, fall out of sockets and are generally just very poor quality.
The safest way to travel around europe is to buy a good quality trailing socket (single or double) with your home country's outlet on one end, good quality cable in the middle and the other country's plug on the other end.
I've seen plenty of recently sold adaptors that get very hot when used with irons and hairdryers (for various standards) as they're totally under rated and prob. never had their rating tested.
Also seen lots of adaptors that wont fit a recessed schuko outlet even though that's what they're supposed to do. BS1363 with unsheathed pins too!
